docs: def _prepare_forms(self):
          """ private function to prepare content for paramType=form
          """
          content_type = 'application/x-www-form-urlencoded'
          if self.__op.consumes and content_type not in self.__op.consumes:
              raise errs.SchemaError('content type {0} does not present in {1}'.format(content_type, self.__op.consumes))
  
          return content_type, six.moves.urllib.parse.urlencode(self.__p['formData'])